In utilizing robotic operators for performing industrial manufacturing, assembling and inspection operations for mass production, it has been found necessary to provide the robotic operators with a mechanical sense of touch or feel in order to simulate the dexterity of the human hand. Robotic operators are increasingly being employed in industrial applications such as for positioning components to be welded on an automotive assembly line, for controlling the movement of cutting and forming tools in machining operations and for applying precisely controlled clamping loads to articles of manufacture during various stages of the fabrication. In such industrial applications, the complex motion of the robotic operator is usually controlled by power actuators such as fluid pressure cylinders with flow of fluid thereto controlled by electrically actuated valves receiving control signals from a microprocessor which responds to force and position input feedback signals from sensors provided on the robotic operator. It has been found particularly desirable to provide continuous electrical feedback signals of the position and magnitude of the forces encountered on the members of the robotic operator for input to the program controlling microprocessor.
Heretofore, the technique employed for providing an electrical signal indicative of "touch" or "feel" for a robotic operator has been to provided a tactile load sensor which utilized an array or matrix of discrete touch pad sensors disposed in a predetermined spaced arrangement in the area of the robotic operator making contact with the work article. One such known tactile sensor is of the type employing an elastomeric pad, or touch surface, having a plurality of moveable rods or plungers attached to the underside thereof. Upon tactile contact of the pad with the work article, the imprint of the work article on the pad is mapped by photo detection of the displacement of the rods and mapping of the location of each rod displaced as it is arranged in the matrix. The location of the displaced rod and the displacement thereof may then be summed; and, the displacement integrated to determine the force print of the work article on the tactile sensing pad. In the aforesaid technique, the optical photo detectors thus provide a continuous electrical readout of the movement of each of the plungers or rods. Such devices are limited in tactile sensitivity by the spring constant of the elastomeric pad with respect to each moveable rod and by the minimum obtainable spacing of the rods within the matrix.
Another technique of providing a tactile load sensing transducer is that of providing a grid or array of electrical wires which are initially separated but are displaced to make contact by pressure exerted on a resilient cover pad. The number of junctions pressed into contact thus gives a map of the work article imprint on the tactile sensing pad. If the pad has predetermined known force deformation characteristics, a microprocessor may be employed to compute the disposition and magnitude of the force sensed by the pad. This type of tactile transducer is similarily limited in sensitivity by the number of discrete electrical junctions which may be provided in a given unit area of surface of the tactile sensing pad.
Still another known technique of providing a tactile sensing transducer is that of employing a nonconductive elastomeric pad separated from a layer of conductive material by a fine screen, or grid, of conductive material. Upon a sensed load being applied to the pad, the resistance of the contact of the elastomeric material with the conductive base within each grid is measured. The number of grids over which contact occurs is mapped thereby enabling a computation of the amount and location of the load sensed by the elastomeric pad over the area of the grid.
Presently, it is also known to provide portions of the computational electronics of the microprocessor in the form of large scale integration (LSI) circuitry disposed below the surface of the conductive base or substrate in the aforesaid sensors employing a conductive resilient elastomeric pad disposed over a nonconductive grid. This arrangement has been found convenient and minimizes the number of circuit connections required for external attachment to the matrix or grid array. In such an arrangement, the circuit for each discreet element of a grid array of the LSI is disposed within the boundaries of a grid element and only a minimum number of interconnections with each grid element circuit is required for connection of the array or matrix to the microprocessor.
The aforementioned known techniques for providing a tactile load sensing transducer have the common disadvantage or limitation that the sensitivity is limited by the load bearing capability of the elastomeric pad, and the number of discreet segments or grid sections which can be disposed within a given contact area of the pad. Thus it has long been desired to find a way or means of providing a tactile load sensing transducer which exhibited a high degree of load sensitivity and nearly infinite resolution of the sensed load position. It has further been desired to provide such a tactile load sensor which provides a continuous electrical signal output indicative of the magnitude and position of the load as experienced by the sensor or transducer.